It wasn't presented to me in the context of mental effects, but of assisting the solidity of the trunk in explosive movement. The idea was the abdominal cavity. The vocal apparatus helps manipulate pressure of the abdomen, through the diaphragm, by putting downward pressure on it, which when combined with pressure from below and the sides, surrounds it with pressure. In the transition between sounds, you can manipulate this into becoming a transition from a pressured state to an even more highly pressured state, and then, why not even the reverse? This is why the end sounds were unimportant, because firstly the goal was not the noise, and secondly because that would ultimately leave the diaphragm locked up and rigid. But even then, this was one limited effect, whereas Moriheu Ueshiba seemed to have a more extensive vocabulary of letters here than two, so I wonder then what he was doing with them or what shapes were implied?

Well, he had a vocabulary of 50 - which grew out of the 5 base vowels, of which we're really just talking about two. Anyway, Kototama can get quite complex, and gets into much more tangled knots than just pressurization (I'm not saying that pressurization isn't important - although I think it can be quite tricky to actually pressurize correctly).